A water tower or elevated water tank is a very large tank constructed for the purpose of holding a supply of water at a height sufficient to pressurize a water supply system. A typical water tower is constructed of either steel, reinforced or prestressed concrete, or brick, and includes a bowl of either spherical or cylindrical shape, is approximately 50 feet (16 meters) in diameter and has a maximum height of approximately 120 feet.
The users of the water supply (a town, factory, or just a building) need to have water pressure to maintain the safety of the water supply. The height of the tower provides the hydrostatic pressure for the water supply system and it may be supplemented with a pump. The volume of the reservoir and diameter of the piping provide and sustain flow rate.
When the water level in a true elevated tank drops to the bottom of the elevated bowl, the tank is essentially empty. The wet center riser pipe, which is no more than 36 inches in diameter, does not qualify as a water storage device. Consequently, the water pressure provided by the true elevated tank drops quickly to zero (0) immediately after the water in the elevated bowl falls to the bottom of the bowl.